(1) Field of the Invention
This invention relates to an apparatus and method for improving the ballistic performance of ammunition round, and, more particularly, the firing sequence of a projectile from an ammunition round.
(2) Prior Art
Telescoped caseless ammunition is comprised of a propellant charge having an axial bore or cavity, a projectile housed entirely within the axial bore of the propellant charge and a primer positioned aft of the projectile. When a telescoped round of caseless ammunition is loaded into the chamber of a gun, the projectile, being housed in a propellant charge, is not seated in the barrel of the gun as is the projectile of a round of conventional ammunition when in a gun chamber. Upon initiation of the primer of the telescoped round, the projectile is forced forward into a barrel of the gun and becomes seated in the barrel. During the time interval from initiation of the primer until the projectile is seated in the barrel of the gun, some of the gases of combustion from the primer and from the initiated propellant charge can escape through the barrel ahead of the projectile resulting in a loss of impetus. Although telescoped ammunition is more convenient to handle than conventional ammunition, it presents different, and often more difficult, design and firing problems.
The primer must perform the dual function of first launching the projectile and then causing the main propellant charge to ignite. If the ignition of the main charge occurs too early, much of the work generated by the burning main propellant charge is lost to gases which escape down the barrel before the projectile obturates the barrel entrance. Should ignition of the main propellant charge be delayed, projectile travel causes the free volume of the chamber to be effectively increased beyond a desired optimum and reduce impetus to the projectile. Therefore, the primer must be formed in a precise, highly reproducible fashion to achieve good performance with telescoped ammunition.
Previous attempts at controlling the ignition and the firing sequence of a telescoped ammunition round have involved the use of adjusting the burning rates or chemical properties of the explosive or propellant materials. For example, it is known to use a gas barrier which separates the propellant charge into a forward section and an aft section. The chemical composition of the gas barrier is such that it momentarily delays flow of hot combustion gas to the forward section of the propellant charge, thereby delaying the ignition of the forward section with respect to the aft section.
However, relying upon the chemical properties of a material makes manufacturing more difficult and expensive because such chemical properties must be accurately controlled to provide performance of the ammunition round within desired limits. Indeed, depending upon the reproducibility required, manufacturing of such ammunition rounds can become an undesirably critical process. Further, it is difficult to develop materials which can cause firing of an ammunition round within a desired time limit under varying temperature conditions. As is known, ambient temperature affects the speed of burning and other chemical reactions. Since ammunition may be required to perform under conditions varying from Arctic cold to desert heat, suitable reliability in chemically controlling an ignition sequence for a telescoped ammunition round has been difficult to achieve.
U.S. Pat. No. 4,197,801, entitled "Ammunition Round" and issued on Apr. 15, 1980 teaches using mechanical, rather than chemical, action to control the firing sequence of a telescoped ammunition round. As a result, there is a high degree of reproducibility of firing action over a broad range of temperatures. Further, the criticality of exactly reproducing the chemical composition of the propellants from batch to batch is reduced thus simplifying manufacture and reducing the cost of manufacture.
This application teaches a propellant charge for supplying firing power for an ammunition round having an axial cavity wherein a control tube selectively covers portions of the propellant charge facing the axial cavity thereby putting a selected portion of the propellant charge in communication with the axial cavity through a firing opening. A projectile is housed within the axial cavity and can be fired from the ammunition round. A primer is positioned generally aft of the projectile means and provides a firing force as part of a firing sequence for firing the projectile from the ammunition round. A piston seal provides a movable barrier between the primer and the propellant charge means. As a result, of the firing of the primer, the piston moves from a position blocking the firing opening through the control tube means to a position forward of the firing opening thus permitting communication from the primer means to the propellant means. However, further movement of the piston is not restricted and the piston is ejected from the ammunition round. The presence of such solid debris is particularly undesirable if the ammunition round is used aboard aircraft. The airplane may be damaged by the debris in various ways including engine failure. These are some of the problems this invention overcomes.